Race Engine Forum UK

Hi Guy,

I wanted to ask for years . Why do you use plasticine around the manifold mating face where the intake ports start when you measure gas flow of a Fiat TC head? Does it have something to do with trumpets/horns to improve flow? What is the difference in measurements with and without the plasticine?

Thanks once again,

If you leave a sharp edge the resulting turbulence (see picture) during inlet flowtest results causes erratic + high flow loss.

The intensity of the turbulence can vary from test to test and so gives 'unrepeatable' results. In other words you get erratic readings when repeating tests that don't make any sense. So it is best avoided. Given that all good engines will (hopefully) run with radiused rampipes, if you don't have an entry radius you are not seeing the thing behaving at its best potential.

GC

Guy,

If a choice of radiused entry was available would there be a particular (ish) radius to aim for?

Nik

Are you referring to the clay for test or rampipe design?

G

Guy,

The ram pipe design interests me. I've dressed the weld off my manifold and eased a small radius onto the entry but stopped short of making it bigger though I nearly did. I've not yet had a gauge on it but intend doing just that when I can get round to a friend who has a set, a couple of pictures is the best I can do for now.





Thanks,

Nik

As a rule of thumb Nik - the bigger the better. The larger the radius - esp into a parallel port section like yours - the less separation you'll get around the curve - exactly like the short side radius in a port.

To prove out what you can 'get away with' (ie: how small you can go) - you need modelling clay and a flowbench, but any rad is better than none. But a simpler method you might be able to adopt is - build a rad into your setup without adding material. Maybe do it by flaring (tapering) the outer region of the entry section (2" in or so) at 15 deg included angle (keeping min 2-3mm wall section thickness) and then radiusing that flare into the existing flat outer area.

FWIW - in the general interest:

As I showed in great detail with flowbench testing the GC Head Prep DVD (which a disappointingly small number of people bought) the entry loss with a good rampipe design (or radiused entry section in this case) should be ZERO! Some examples of good and bad below.

One rampipe design that I always liked was that produced by Pipercross; their range of intake systems is always worth reading and I am pleased to see the importance they place on cold ducted air feed to the manifold - something at last that people are paying attention to. Cold air feed - and I mean fully sealed off - not just a pipe 'spraying' cold air into the intake region (!) and close attention to entry section (ie: rampipes and things of that type) give the closest I know to CHEAP HORSEPOWER!

http://www.thepipercrossshop.co.uk/comp ... mpipes.asp

G

Guy,

Thanks for an excellent explanation and pictures, I can feel the grinders going to be out again. I haven't the meat in the runners to form the taper I'd like but there's a little thickness to work in each entry especially in the lowest point of the plenum. This inevitably will lead to the entry being oval in shape (even more so than it already is). This won't matter a bit will it? I'm imagining that the air entry into the runner is eased naturally by the shape of my plenum at the highest points but hindered by the flat floor so the more I can radius the floor and taper the runner at this point the better?

Slightly off topic but based around the runner cross section (trying my best to taper it) I'm considering trying to take a mould of the runners so I can map the cross section. Have you any experience of doing this? I'm trying to find a product to use without luck.

Nik

Latex mould?

http://themodelmakersresource.co.uk/art ... le006.html

?

G

I've been searching for a supplier in the UK of something along the lines of this http://www.smooth-on.com/Rigid-and-Flex ... index.html which I'm led to believe is good for this very task, not the best quality mould but quick and easy with a decent ability to be sliced up. The taper intrigues me and I can't think of an easier way of mapping it accurately.

Regards,

Nik